Meiotic maturation is unique to oocytes and of reproductive importance since it is requisite for fertilization and normal development. In addition, resumption of meiosis affords an alternative system to study regulation of the G2 to M transition in the cell cycle since oocytes, naturally arrested in a G2-like state, undergo a G2 to M transition. Knowledge of factors controlling the cell cycle is vital for understanding regulation of cell growth and division. In oocytes obtained from vertebrates cAMP appears involved in mediating meiotic arrest and a drop in oocyte cAMP is correlated with resumption of meiosis. We have recently obtained results implicating a calmodulin-dependent step, as well as changes in protein phosphorylation in meiotic maturation of mouse oocytes. We propose to extend our studies on regulation of meiotic maturation by (1) observing the effect on meiotic maturation of mouse oocytes microinjected with substances that will (a) perturb oocyte cAMP levels, (b) inhibit calmodulin function and (c) perturb the state of protein phosphorylation; (2) determining if oocytes possess a cAMP-dependent protein kinase; and (3) determining the existence and role of mouse oocyte maturation promoting factor in oocyte maturation. Results from the proposed experiments will clarify the mechanism and temporal sequence of events involved in meiotic maturation of mammalian oocytes and may be generalized to regulation of the G2 to M transition in the cell cycle.